Field of the Invention
The present application is related to circuits and more particularly to control circuits for high-power applications.
Description of the Related Art
In a typical control application, a processor system provides one or more control signals for controlling a load system. During normal operation, a large DC or transient voltage difference may exist between the domain of the processor system and the domain of the load system, thus requiring an isolation barrier between the processor system and the load system. For example, one domain may be “grounded” at a voltage which is switching with respect to earth ground by hundreds or thousands of volts. Accordingly, an intermediate system includes isolation that prevents damaging currents from flowing between the processor system and the load system. Although the isolation prevents the processor system from being coupled to the load by a direct conduction path, an isolation channel allows communication between the two systems using optical (opto-isolators), capacitive, inductive (transformers), or electromagnetic techniques. However, the intermediate system typically uses a voltage converter and output driver to provide the control signal at voltage levels suitable for the load system.
Referring to FIG. 1, in an exemplary motor control application, processor 100, which may be a microprocessor, microcontroller, or other suitable processing device, operates in a first domain (i.e., VDD1, e.g., 5 Volts (V)) and provides one or more signals for a high power load system operating in a second domain (i.e., VDD2, e.g., 600V). Systems 102 each include an isolation barrier 130 and a communication channel for safely communicating control signals from processor 100 to drivers 106, which drive high-power drive devices 108 of a three-phase inverter used to deliver three-phase power to motor 120. Exemplary high-power drive devices include power metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated-gate bipolar transistors (IGBTs), Gallium-Nitride (GaN) MOSFETs, Silicon-Carbide power MOSFETs, and other suitable devices able to deliver high currents over short periods of time.
Voltage converters 104 convert an available power supply voltage from VDD2 to a voltage level (i.e., VDD3, e.g., 24V) usable by a high side of systems 102 and drivers 106. Note that in other embodiments, a single voltage converter 104 converts one power supply voltage from a first voltage level (e.g., VDD2) to multiple other voltage levels (e.g., VDD1 and VDD3) and/or provides multiple outputs of a particular voltage (e.g., multiple VDD3 outputs corresponding to multiple systems 102). Drivers 106 provide switch control signals at levels required by corresponding high-power drive devices 108 of the three-phase inverter. The load motor requires three-phase power at high power levels. Systems 102 that correspond to high-power devices coupled to VDD2 (high-side inverter devices), are “grounded” at a voltage that is switching with respect to earth ground by the high voltage levels of VDD2.
Typical high power devices 108 of the three-phase inverter that are used to drive motor 120 require substantial turn-on voltages (e.g., voltages in the range of tens of Volts) and are susceptible to fault conditions that may damage those devices. For example, when a short circuit current condition exists, that is, both devices of an individual inverter are on, high current flows through those devices, which may destroy them. Accordingly, fault detection techniques detect this desaturation condition. System 102 may send an indicator thereof to processor 100, and system 102 or processor 100 may trigger a shut-down of a corresponding device. However, if a high-power drive device 108 is shut-off suddenly, large di/dt induced voltage spikes may occur in the motor control signal. Such voltage spikes could be damaging to the drive circuit and/or load. Accordingly, flexible techniques for handling faults without damaging high-power drive devices or the load which those devices control are desirable.